November 12-13, 2020 Tudelft.zoom.us/j/3022518030

Keynote02A New Design Model for Welded Joints - Experimental and NumericalInvestigations of Welds at High-Strength SteelsRichard Stroetmann, Thoralf KästnerTechnische Universität Dresden, GermanyE-mail: Richard.Stroetmann@tu-dresden.deThe use of high-strength steels offers economic and ecological advantages. However, in weldedconstructions some of these advantages are partly compensated by conservative design rules and amore extensive execution. A disadvantage in the system for determining the load-bearing capacity ofwelds according to Eurocode 3 parts 1-8 and 1-12 is that the dependencies on the base and fillermaterial, the welding process (cooling time t8/5), the type of stress (tension, compression, shear andtheir combinations) and the joint type are summarized in a correlation factor βw.The influence of the peak temperature and the cooling rate on the microstructure and mechanicalproperties of the heat-affected zone was investigated using dilatometer tests. The different behavior ofquenched and tempered steels and thermomechanical rolled steels with their alloying concepts andhardening mechanisms became clear. The results provide the basis for the evaluation of the heataffected zone with regard to its softening or hardening at different process parameters.In the planned contribution the experimental and numerical investigations of the research projectP1020 and the methodology used for this purpose will be presented. The results will be illustrated anddifferences to existing design models will be explained. Furthermore, recommendations for thepractical execution of welded joints on high-strength steels will be formulated.12Member and JointWithin the scope of the AiF-FOSTA research project P1020, basic principles for a substantialimprovement of the design and execution rules for welded joints on high-strength steels weredeveloped. For a new design model for welded joints a flat tensile test was designed to determine thestrength and ductility of welds in a simple manner under the given execution parameters. Furthermore,extensive experimental and numerical investigations were carried out on typical joints and the designmodel was calibrated. Despite the greater differentiation in the design and the possibilities created forthe execution, the calculation effort remains low.

Abstract04Welded Connections in Innovative High Strength Steel ConstructionsJennifer Spiegler, Ulrike KuhlmannInstitute of Structural Design, University of Stuttgart, GermanyE-mail: Jennifer.Spiegler@ke.uni-stuttgart.de, Ulrike.Kuhlmann@ke.uni-stuttgart.deIn Europe, the majority of steel structures steel is realized in S235 and S355 steel grades. In additionto the common steels, high performance steels up to steel grade S700 (and more) are available withgood weldability and a high ductility which allow slender and aesthetic structures. However, for theparticular situation of joining High Strength Steel (HSS) elements the present design rules, e.g. inEN1993-1-8 are in many cases inadequate because the recent rules were developed for standard steelsand then transferred to High Strength Steels. In the frame of several research projects including a highnumber of tests for fillet welds a realistic and coherent design model for the determination of the loadcarrying capacity of welded connections made of HSS has been developed and meanwhile is acceptedfor the future version of Eurocode 3.13Member and JointFor butt welds made of HSS an adjustment of the present design rules has not yet been carried out.The current design rules according to EN1993-1-8 require a verification of the adjacent sections of themember only. However, depending also on the shape of the butt weld, the welding technology and theweld procedure the failure may occur in the area of the weld and not at the adjacent member section.Therefore, the actual load carrying capacity may be lower than the calculated one resulting in the riskof premature failure. A German research project has been finished with the objective to investigate buttwelds made of HSS under various influence parameters in order to avoid a premature failure and todevelop a modified design resistance function for butt welds on HSS. In order to guarantee and promotean economic, future-oriented and resource-saving application, it is necessary to develop efficientdesign methods and processing guidelines also for butt welds. On the basis of the investigations of theresearch project, a new design resistance function could be developed that meets exactly theserequirements.

Abstract05Stub Column Behaviour and Design of High Strength CircularConcrete Filled Steel TubesJunbo Chen, Tak-Ming ChanDepartment of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Hong KongE-mail: jun-bo.chen@connect.polyu.hk, tak-ming.chan@polyu.edu.hkKey Words: High strength steel; High strength concrete; CFST; Short columns.14Member and JointThis paper presents a comprehensive experimental investigation into the stub column behaviour ofhigh strength circular concrete-filled steel tubular (CFST) columns. A test database composed of 232results was firstly compiled to review the state-of-the-art of high strength circular CFST columns.Subsequently, a total of 36 stub column specimens were tested. The steel tubes have a diameter over150 mm and with various diameter-to-thickness ratio D/t are considered. The steel tubes werefabricated from Q460, Q690 and Q960 quenched and tempered steel plates, and three concrete gradeswith target concrete cylinder strengths of 30, 50 and 90 MPa were used to fill the steel tubes. Detailedtest results, in terms of failure modes and axial load versus axial strain responses of the stub columns,are fully presented and discussed. The experimental results were employed in conjunction with thecollected data to evaluate the applicability of current codified design methods in American standard,Eurocode, Australian/New Zealand standard, Chinese code and Japanese recommendation to thedesign of high strength circular CFST stub columns. The effectiveness and consistency of theestimations from each code is thoroughly discussed.

Abstract06Testing, Simulation and Design of HSS Tubular MembersXin Meng, Leroy GardnerDepartment of Civil and Environmental Engineering, Imperial College London, London, United KingdomE-mail: xin.meng15@imperial.ac.uk15Member and JointAs the yield strength increases, the influence of residual stresses and geometric imperfections tends toreduce, and more favourable buckling behaviour is therefore anticipated from high strength steeltubular members. However, this effect is not systematically accounted for in current internationaldesign standards. The structural behaviour and design of hot-rolled and cold-formed high strength steelcircular, square and rectangular hollow section (CHS, SHS and RHS) columns are addressed in thispresentation. A series of experiments was firstly conducted – twelve cold-formed S700 CHS columnsand twelve S690 and S770 SHS column specimens were tested under axial compression with pinended boundary conditions. Finite element (FE) models were developed to replicate the experimentalresults and to carry out parametric studies to expand the column buckling data pool over a wider rangeof geometries and steel grades. Shortcomings in the existing buckling design rules in the European,North American and Chinese codes, particularly in the higher yield strength domain, were highlightedthrough comparisons with the test and FE results. To address these shortcomings, a modified Eurocode3 (EC3) approach was proposed; the new approach features a reduced plateau length and animperfection factor that is a continuous function of yield strength, reflecting the reducing relativeinfluence of residual stresses and global imperfections with increasing steel grades. Improvedconsistency in resistance predictions over the existing design provisions is demonstrated across a widerange of steel grades and relative slenderness values. Finally, the reliability of the design proposal wasstatistically verified in accordance with EN 1990.

Abstract07Experimental study of X-joints made of HSSHagar EI Bamby1, Rui Yan1, Kristo Mela2, Milan Veljkovic11. Delft University of Technology, Netherlands2. Tampere University, FinlandE-mail: m.veljkovic@tudelft.nlHigher strength steels hollow sections with yield strength higher than 460 MPa are becomingincreasingly competitive in long-span structures. Reduction of self-weight accomplished with thesmaller wall thickness of the hollow section, is leading to fabrication, transportation and executionbenefits. The use of HSS has a positive effect on CO2 equivalent emission reduction related to the usedmass of material for a functional unit. Such characteristic, aligned with a plan towards a modern,resource-efficient and competitive economy, is important for the future development of theconstruction sector. However, a lack of experimental evidence for the design of hollow section jointsis identified as one of the main reasons to propose material factors in the revised version of EN19931-8. The material factors are perceived as a rather pessimistic value. In the revised version materialreduction factors (Cf 0,8) for the design of joints made of steel with a yield strength larger than 460and up to S700 is given.16Member and JointIn this paper, the behaviour of the X-joints made of S355, S500 and S700 are investigated and theproposed material reduction factors are discussed. Seven full-scale welded X-joints in tension withrectangular hollow sections were tested in Stevin Lab II, TUD. Additionally, dog-bone couponspecimens were tested in order to obtain the engineering stress-strain relationship of the material.Based on the results of coupon tests, finite element model (FEM) is used to model X-joint experiments.Furthermore, results of a short parametric study are presented in which effect of three parameters: theyield strength, the parameter β (brace width over chord width ratio) and the thickness of the profilesare considered in predicting characteristic resistance of X-joints. Finally, conclusions are drawn on thevalidity of the material reduction factors.

Abstract08Tests and Numerical Simulations of HSS Stiffened Curved PanelsSara Piculin, Primož MožeFaculty of Civil and Geodetic Engineering, University of Ljubljana, SloveniaE-mail: primoz.Moze@fgg.uni-lj.si, sara.piculin@fgg.uni-lj.siThe use of curved steel panels in bridge design has been increasing in the last twenty years but thedesign recommendations and the general knowledge in this field remain scarce. To address this issue,nine large-scale tests were performed on longitudinally and transversally stiffened plates made of highstrength steel (S500, S700). They were subjected to compressive stresses up to collapse. The specimenscomprised of curved (7) and flat (2) plates that differed in material grade and geometric parameters,such as panel thickness, aspect ratio, size and shape of stiffeners. The curved edges of the specimenwere fixed; longitudinal edges were simply supported. The initial geometry of the specimens wasmeasured by a structured light portable 3D scanner. Moreover, a numerical model built in the generalpurpose code ABAQUS is presented and verified against the test results regarding initial stiffness,ultimate resistance and failure mode. Numerical simulations, based on the test panel geometry, themeasured initial geometric imperfections and elasto-plastic material characteristics from tensile tests,demonstrate very good agreement with experimental results.Furthermore, a verification procedure for curved stiffened panels is proposed that gives a goodestimation of the maximum loads obtained from experimental and numerical tests. The procedure is inline with the design methodology of EN 1993-1-5, accounting also for panel curvature.17Member and JointAll specimens showed a linear elastic response up to a high load level. After local buckling failure,bending deformations were observed for flat panels due to the additional bending moment arising fromload eccentricity. Higher section modulus prevented bending failure of curved specimens, for whichlocal collapse mechanism prevailed in all cases in combination with torsional buckling of longitudinalstiffeners. For stockier panels, the ultimate load was mainly driven by the combination of localbuckling and yielding of the material. For panels with higher slenderness, collapse behaviour wasgoverned by elastic buckling and post-critical strength reserve.

Abstract09On the Rotation Capacity of High Strength Steel BeamsHelen Bartsch, Felix Eyben, Gesa Pauli, Simon Schaffrath, Markus FeldmannRWTH Aachen UniversityE-mail: h.bartsch@stb.rwth-aachen.de18Member and JointTo design efficient and highly utilised sections, the plastic/plastic design is a powerful approach. Interms of plastic design, Eurocode 3 requires only Class 1 cross-sections and steel grades up to S460,which are conventional strength steels (CSS). High strength steels (HSS) with yield strengths up to700 MPa are not considered suitable for plastic design due to their lower ductility. However, theexclusion of HSS seems unnecessary considering recent test results. Experimental investigations werecarried out on 20 homogeneous and hybrid high-strength double-symmetric I-section girders withdifferent slenderness properties of flange and web and different spans. It was found that the rotationrequirement of R 3, which is currently implicitly required by EC3 regulations, can indeed be achievedby high strength steel beams depending on their cross-sectional properties. The experimental tests werealso numerically recalculated. Material properties of the models were defined by flow curves, whichwere first calibrated on the basis of small-scale tensile tests and then slightly adapted to the results ofthe full-scale tests. The failure of ductile material in terms of crack initiation and development is takeninto account by including a damage mechanics model. It can be shown that experimental and numericalresults show a very good agreement. In addition, a numerical parametric study was carried out, whichincludes more than 800 simulations with different slenderness values of flange and web, steel grade,loading situations, lateral support characteristics as well as different characteristic material properties.The rotation capacity values of the different beams were compared with the rotational requirements oftypical systems. As a result, design recommendations for the plastic design of HSS girders are given.

Keynote03Apply the High Strength Steels to Enhance the Robustness of BuildingFrames in Seismic Areas. The Dual Steel ConceptDan DubinaPolitehnica University/ Romanian Academy Timisoara Branch, RomaniaE-mail: dan.dubina@ct.upt.roIn terms of structural mechanics, a robust structure is the one characterized by high redundancy. Thatcan be achieved by appropriate design, providing a proper conception and , aiming to ensure a goodbalance between stiffness, overstrength and ductility of structure components, in order to securemultiple routes for force transfer, to allow the stress redistribution when the plastic zones are developed,and supply sufficient strength of the members having the mission prevent the collapse.That is this is the Dual Steel Concept.When braced frames of removable MCS dissipative members are used, such as the Dissipative Linksin EBF , Buckling Restrained Braces in CBF or Shear Walls in MRF systems, the elastic HSS part ofthe structure has a beneficial restoring effect after earthquake enabling to replace the “fuses” andrecover the initial shape. Such a type of structural solution enables for an easy repair of the given afterearthquake, which can gain its operationality in shorter time.That is seismic resilient solution.Dual-Steel concept can be considered for beam-to column connections, too, if apply the samephilosophy related to the role of ductile and brittle components. However, of a higher seismic demand,when plastic incursions might develop in the HSS members, the properties of material have to becarefully controlled, and advanced analyses have to be conducted using properly cyclically calibratedmaterial properties. Moderns steels of grades S 460 up to S690, still possess some usable ductility, theycan be used, A Performance Based Design can by applied to calibrate designed structural parametersto satisfy the seismic demand,This is a review paper, which summarized the results obtained in several National and RFCS researchprojects, focused on this topic, by the team of Department of Steel Structures and Structural Mechanicsfrom the Politehnica University of Timisoara.19Seismic BehaviorModern seismic design codes have already implemented these principles. A dissipative structure, incase of a severe earthquake, possess in the dissipate zones ductile components designed to undergoplastic deformation, and has the capacity to transfer stresses in the adjacent zones, while the structurestands-up (e.g. collapse prevention), due to the overstrengthened components, designed to remainpredominantly elastic during earthquake. That is the capacity design principle. The members designedto remain elastic during earthquake, such as columns, are responsible for robustness of the structureand prevention the collapse, being characterized by a high strength demand. The ductile components,e.g. plastic members, realized by Mild Carbon Steel (MCS) have the mission to dissipate the seismicenergy, acting like “structural fuses”. By a correct application of Capacity Design principle, aneffective seismic resistant framing solution can be obtained by combining HSS- S460 to S690 (700),and MCS (S235 to S355).

Abstract10Seismic Performance of High-Strength Steel Fabricated Framed-TubeStructures with Replaceable Shear LinksMing Lian1,2, Mingzhou Su1,2, Binlin Guan1, Hao Zhang1, Qianqian Cheng11. School of Civil Engineering, Xi’an University of Architecture & Technology, Xi’an 710055, China2. Key Lab of Structural Engineering and Earthquake Resistance, Ministry of Education (XAUAT), Xi’an 710055, ChinaE-mail: lianming@xauat.edu.cn20Seismic BehaviorIn steel framed-tube structures (SFTSs), deep spandrel beams that have large cross sections withflexural plastic hinges at beam-ends cannot be adequately developed, which is the reason why SFTSspresent lower ductility and energy dissipation capacities. To address this issue, high-strength steel(HSS) fabricated SFTSs with replaceable shear links (HSS-SFTS-RSLs) have been proposed. In HSSSFTS-RSLs, shear links are made of conventional steel and are placed in the middle of the deepspandrel beams to act as ductile fuses to dissipate seismic energy. The seismic performance andperformance-based seismic design method of HSS-SFTS-RSLs are studied due to experimental tests,numerical simulation, and theoretical analysis. The results

steel, weathering steel, fire-resistant steel, high-toughness steel, low-yield-point steel, memory alloy steel, additive manufacturing steel and other types/grades of steel used in construction different from low grade carbon steel. Currently, the council focuses on the structures made of HPS and their joints using bolted and welded connections.